DE3143372C2 - Process for the electronic evaluation of the Korotkoff noises occurring when measuring blood pressure according to the Riva-Rocci method - Google Patents

Abstract

A method and a device are proposed for the electronic evaluation of the Korotkoff noises occurring when measuring blood pressure according to the Riva-Rocci method. In order to obtain a specific signal which corresponds to the systolic blood pressure value and the Korotkoff sound corresponding to the diastolic blood pressure value, a frequency analysis of the frequency spectrum of the Korotkoff noises takes place. For this purpose, one makes use of the determination of the changes in the frequency spectrum of the Korotkoff sounds characteristic of the systolic and diastolic blood pressure values. A device for carrying out the method has an amplifier (14) which is connected to a microphone (12) and to which a plurality of bandpass filters (16, 17, 18) that are interconnected on the input side and matched to different frequency ranges are connected. A rectifier circuit (19, 20, 21) follows each band-pass filter. Two rectifier circuits each are connected to a device for forming quotients (25, 26), and each device is followed by a discriminator (27, 28). The discriminators are followed by a control logic (29) which supplies a signal voltage for controlling the display of the systolic and diastolic blood pressure values. According to a further development of the invention, use is made of the Fast Fourier Transformation in the evaluation.

Description

5. Apparatus according to claim 4, characterized in that the amplifier (14) is a controllable amplifier, the gain of which is influenced by a control voltage (Ur) which is derived from the output voltages of the rectifier circuits (19, 20, 21).

6. Apparatus for performing the method according to claim 3, characterized in that an amplifier (51) connected to a microphone (50) is followed by an anti-aliasing low-pass filter (52), which is followed by an analog-to-digital converter (53) that is connected to the analog-digital converter is followed by a digital filter (54) and then an electronic memory (55) and that a microcomputer (57) is provided, the first input (56) of which with the memory (55) and the second input (58) with a read-only memory (59) and which controls the digital filter (54) and the electronic memory (55) via an ω connection (62) and emits a signal voltage at its output (60) to control the display of the systolic and diastolic blood pressure values.

The invention is based on a method according to the preamble of the main claim.

In electronic blood pressure measuring devices that work according to the Riva-Rocci method, is already known (DE-AS 29 45 126) to evaluate the Korotkoff noises in such a way that one of the entire. Frequency band of the noises unfold a narrow frequency band and the associated amplitude values determined by means of a downstream visual circuit logic the Korotkoff noise that occurs first during the measurement with falling cuff pressure and determine the last Korotkoff sound that occurred and thus the systolic and diastolic Determine blood pressure value. In addition, special measures can be used to hide background noises will. However, this known measuring method is susceptible to interference which reduces amplitude. For example, an unfavorable positioning of the microphone used to listen to Korotkoff noises calls out such disturbances.

Advantages of the invention

The inventive method with the characterizing features of the main claim has the advantage that the blood pressure values based on the frequency spectrum of the Korotkoff sounds and the changes this spectrum can be determined. This allows the Korotkoff noises to be better recognized, and the measurement accuracy of electronic blood pressure meters increases. Other advantages are: that the measurement result does not depend as strongly on the position of the microphone as with the known electronic Blood pressure measuring devices and that artifacts are better suppressed.

The measures listed in the subclaims are advantageous developments and Improvements to the procedure specified in the main claim are possible. That according to the invention is particularly advantageous Procedure if the evaluation is carried out by comparing the amplitudes of the frequency range by frequency range Korotkoff noise frequency spectrum and by determining the for the systolic and the diastolic Blood pressure value characteristic changes in the amplitude ratios takes place then namely can the evaluation can be carried out with relatively simple means.

There is also a blood pressure measuring device with a microphone known (DE-OS 30 14 219), in which it is determined by filter means whether a certain frequency prevails in the respective Korotkoff noise. The specific frequency depends on whether the fourth or fifth Korotkoff sound is used as the criterion for the presence of the diastolic or systolic Blood pressure should be decisive. The filter means can be switched to different frequencies will; however, only a single filter frequency is used in a measurement. One Frequency analysis of the frequency spectrum therefore does not take place.

drawing

Exemplary embodiments of the invention are shown in the drawing using two figures and in FIG explained in more detail below. The drawing shows in

Fig. I is a block diagram of an inventive

Device for evaluating Korotkoff noises in a first embodiment and

F i g. 2 shows a block diagram of a device according to the invention for evaluating Korotkoff noises in a second embodiment.

Description of the invention

One shown in FIG. i denoted by 10 evaluation device for evaluating Korotkoff noises in the electronic blood pressure measurement according to the Riva-Rocci method belongs to a blood pressure measuring device and is connected with its input IJ to a microphone 12, for example a structure-borne sound microphone. The microphone is housed in an inflatable blood pressure cuff 13. The input 11 of the evaluation device is connected to the inputs of several bandpass filters 16, 17, 18 via a controllable amplifier 14, which has a connection 15 for supplying a control voltage Ur. For the sake of clarity, FIG. 1 shows only three bandpass filters which are designed for two adjacent frequency ranges F1 and F2 and a more remote frequency range Fi of the Korotkoff noise frequency spectrum. The dashed line between the band filters 17 and 18 is intended to indicate that if necessary more than three, that is to say generally π bandpass filters for π frequency ranges, can be present. A rectifier circuit 19, 20 and 21 follows each of the bandpass filters.

In each case two rectifier circuits, for example 19, 20, supply a second DC voltage to a device to form the quotient 25, 26, which each have a discriminator 27, 28 with a control logic 29 in Connection. An output 30 of the control logic simultaneously forms the output of the evaluation device 10. A pressure gauge 31 is connected to the output 30, which is for example a two-digit manometer. Instead of of the two-pointer manometer, a single-pointer manometer can also be used, on which with the help an optical and / or acoustic signal from a display device 32 the systolic and the diastolic Blood pressure value can be read.

The device according to Fig. 1 functions as follows:

First, the blood pressure measuring cuff 13 is put on and inflated to a pressure value greater than the systolic blood pressure value. Then you let the Air will slowly escape from the cuff. As a result, Korotkoff noises occur. The from Korotkoff noises or sound signals recorded by microphone 12 have different frequencies on that in a Korotkoff noise frequency spectrum lie, which includes, for example, frequencies between 20 Hz and 250 Hz

The Hall signals converted into electrical signals by the microphone are amplified in the controllable amplifier 14 and then divided into frequency ranges Fi, F1 and FZ by means of the bandpass filters 16, 17 and 18. The frequency range F1 includes, for example, frequencies between 18 Hz and 22 Hz, the frequency range F 2 frequencies between 28 Hz and 35 Hz and the frequency range F3 frequencies between 180 Hz and 220 Hz.

The output voltages of the bandpass filters 16, 17, 18 are rectified in the rectifier circuits 19, 20, 21. From the rectified voltages, the control DC voltage Ur is derived by means of the network 22, which ensures that the Korotkoff signal voltages at the output of the controllable amplifier 14 also have certain amplitude values in the event of incorrect positioning of the measuring cuff 13 or the microphone 12.

The output from the rectifier circuits

ίο DC voltages are paired in the devices to form the quotient 25, 26 compared with one another. Is it certain, for example, that the systolic Corotkoff noise corresponding to the blood pressure value, the output voltages of the rectifier circuits 19, 20 are fundamentally in a certain relationship to one another, that of the relationship the output voltages can differ from other rectifier circuit pairs, the pre-rolled discriminator 27 determined whether this Ratio for the Korotkoff sound just recorded is present Only with this specific ratio does the discriminator 27 give a first specific one Signal voltage to the control logic 29 from this then causes, for example, that a pointer of the as Two-digit manometer trained pressure gauge 31 is held mechanically and continues despite the The systolic blood pressure value is stored in the measuring cuff as the pressure drops.

For example, it is also established that the Korotkoff sound corresponding to the diastolic blood pressure value the output voltages of two other rectifier circuit pairs in a given one Ratio, this ratio is used in a further device for the formation of quotients, for example 26, formed and determined with the discriminator 28 whether the specific relationship is present. Provided If this is the case, the discriminator 2S outputs a second specific signal voltage to the control logic 29, which causes the second pointer of the two-digit manometer to be locked and thus shows the diastolic blood pressure value.

The criterion for either the systolic or the diastolic Korotkoff sound corresponding to blood pressure value can also have more than two frequency ranges include. In this case, the control logic 29 must the simultaneous occurrence of signal voltages to the Recognize the outputs of several discriminators.

The evaluation of the Korotkoff noise does not have to be based on the audible part of the Korotkoff noise frequency spectrum restrict. The frequency spectrum also contains Korotkoif noises in the infrared range Features, for example deep minima, the frequencies of which are particularly close to the characteristic shifting of the diastolic blood pressure value.

If only a single-pointer manometer or a digital display without memory is provided, both of them have the effect Signal voltages, for example, switching on a first and a second optical and / or acoustic signal Signal that causes the user of the Blu'.drackmesser to display the signals displayed when the signals occur To iotate measured values for the systolic and diastolic blood pressure.

In another embodiment of the evaluation device, digital bandpass filters are used Microcomputer circuit then switches the filters and carries out a frequency analysis on digital

ge. The structure of such a circuit is known in principle to the person skilled in the art, so that a circuit diagram and circuit details can be dispensed with.

The number of frequency ranges F1 ... or the required The filter depends on the required evaluation accuracy. This becomes greater, the more physiological peculiarities are recorded.

From a certain number of frequency ranges onwards, it is advisable to use the so-called »Fast Fourier Transformation «(FFT) to be applied. As a result, the number of components can be reduced.

Using the block diagram in FIG. 2 shows how the FFT principle is used in an electronic blood pressure monitor can be applied.

The circuit comprises a microphone 50 which is contained in a blood pressure measuring cuff and which is connected to a controllable! Amplifier 5! verbund? "is to which an anti-aliasing low-pass filter is attached 52 connects. The filter 52 is followed by an analog / digital converter 53, a digital filter 54 and an electronic memory 55 which is connected to a first input 56 of a microcomputer circuit 57 is. A second input 58 of the microcomputer circuit is connected to a read-only memory 59, this is preferably a ROM (Read Only Memory) circuit. The microcomputer 57 has one Output 60, at which it emits signals for controlling a pressure gauge 61. Via a connection 62 controls the microcomputer, the controllable amplifier 51, the digital filter 54 and the electronic memory 55.

The circuit according to FIG. 2 has the following functions.

The microphone 50 converts the recorded Korotkoff noises into an alternating voltage. This voltage is amplified in the controllable amplifier 51 and then the anti-aliasing low-pass filter

52 fed The filter 52 prevents higher frequencies - in the vicinity of the clock frequency of the analog-to-digital converter 53 - lead to ambiguities in the digital signal path. The cutoff frequency of the low-pass filter 52 is above the highest frequency to be expected in the Korotkoff noise.

The output voltage of the filter 52, which is present in analog form, is converted to the analog-digital converter

53 converted into a corresponding digital value In the digital filter 54, which is processed by the microcomputer 57 is controlled, the spectral decomposition of the Korotkoff noise takes place. The entire spectrum or for the blood pressure measurement important parts of the frequency spectrum of the current Korotkoff sound are stored in the memory 55 and entered once in the read-only memory 59 with the Setpoint values are compared with the aid of the microcomputer circuit 57. Systolic and diastolic blood pressure are again based on the amplitude ratios of Korotkoff noise components from different spectral ranges and identified by the change in the amplitude ratios at the output 60 of the microcomputer 57 output control signals are finally the displays and possibly the Functional processes of a blood pressure meter controlled

1 sheet of drawings

Claims (4)

Patent claims: 1. Method rum electronic evaluation of the Korotkoff noises occurring in the blood pressure measurement according to the Riva-Rocci methods and for generating a specific signal each for the Korotkoff sound corresponding to the systolic blood pressure value and the Korotkoff sound corresponding to the diastolic blood pressure value, characterized in that the determination of the specific Signals by frequency analysis of the Korotkoff noises and by determining the changes in the frequency spectrum characteristic of the systolic and diastolic blood pressure values are carried out ι c 2. The method according to claim 1, characterized in that the evaluation by comparing the Sound amplitudes of the Korotkoff noise in different frequency ranges and by determination the changes in the blood pressure characteristic of the systolic and diastolic blood pressure the amplitude ratios takes place 3. The method according to claim 1 or 2, characterized in that that the evaluation by comparing the sound amplitudes of the Korotkoff noises is carried out digitally through "Fast Fourier Transformation" (FFT). 4. Apparatus for carrying out the method according to claim 1 or 2, characterized in that a plurality of input side interconnected, and an input connected to a microphone (12) amplifying · (14) on different frequency ranges (FX ...) tuned bandpass filter (16, 17 , 18) follow that each filter is followed by a rectifier circuit (19, 20, 21) Lt. that at least two rectifier circuits are connected to a device for quotient formation (25, 26), that a discriminator (27, 28) is connected to each device for quotient formation and that the discriminators are connected to a control logic (29) which supplies a signal voltage to Controlling the display of the systolic and diastolic blood pressure values provides.